Biting screw driver

ABSTRACT

A screw driver having a foot portion on the lower extremity of its blade for increasing the effectiveness of the blade in griping the sidewalls of a screw slot.

United States Patent 1191 1111 3,923,088

Arnn Dec. 2, 1975 BITING SCREW DRIVER 2,676,510 4/1954 Hodell 145/50 A x 2,808,087 /1957 Vaughn 145/50 A [76] Inventor. Edward T. Arnn, 406 Club Lane, 2'994354 8/1961 Vaughn h M [/50 A St Matthews, y- 40207 3,026,920 3/1952 York 145/50 A I YOl'k A [21] Appl. No.1 491,361

Related U.S. Application Data [63] Continuation-impart of Ser. No. 473,840, May 28,

1974, Pat. No. 3,897,812. a

Primary Examiner-Francis S. Husar Assistant Examinr-Marc R. Davidson [52] U.S. Cl 145/50 A [57] ABSTRACT [51] Int. Cl. B25B 15/02 Field Of Search 145/50 A, R A screw driver having a foot portion on the lower extremity of its blade for increasing the effectiveness of References Cited the blade in griping the sidewalls of a screw slot.

UNITED STATES PATENTS 1,479,506 l/l924 Kelleman /50 A UX 2 Claims, 13 Drawing Figures US. Patent Dec. 2, 1975 Sheet 1 of3 3,923,088

US. Patent Dec. 2, 1975 Sheet 2 of3 3,923,088

Sheet 3 0f 3 US. Patent Dec. 2, 1975 1 BITING SCREW DRIVER CROSS REFERENCE TO RELATED APPLICATION This application is a continuation in part of U.S. patent application Ser. No. 473,840 filed May 28, 1974 now U.S. Pat. No. 3,897,812.

BACKGROUND OF THE INVENTION It has been long recognized that present day screw drivers fall far short of being adequate to insert or remove screws which have substantial resistance to turning. Most typically, if a screw has a substantial resistance to being turned, upon applying a torque thereto,

the screw driver blade slips upwardly out of the slot in the screw head. This slippage is an undesirable result arising from the current screw driver blade geometry. Many attempts have been made to modify screw driver blades to make them perform better when in use on difficult-to-turn screws. Representative of these attempts are U.S. Pat. Nos. 3,236,275; 2,684,094 and 370,255. Generally, these attempts have included modifying the screw head, as well as the screw driver blade. However, modification of the screw head is impractical, since screws currently in use do not have modified heads and industry acceptance of any modification is a major obstacle. Another approach is to modify the screw driver blade by providing ribs which project downwardly on each side of the screw head as shown in U.S. Pat. No. 697,836. However, such a screw driver is generally unacceptable since the screw head must be protruding above any adjacent surfaces in order for the screw driver to be used. The invention of this application is a rugged, inexpensive, readily constructed and easily employed screw driver which overcomes all of the defects of prior art screw drivers.

SUMMARY OF THE INVENTION The present invention relates to a screw driver including a preselectively shaped torque transmitting blade which terminates in a lower foot portion which in turn provides a gripping means. The gripping means imbeds itself into the sidewalls of the slot in a screw head to prevent the blade from slipping out of the slot as the screw driver is turned.

More specifically the invention includes a screw driver comprising a shank portion and a blade portion integral therewith, the blade portion terminating at its free end in a foot portion, said foot portion being integral with said blade and being generally isoscelestrapezoidal in cross section with its widest base portion lying in a plane generally perpendicular to the axis of said shank and being engagable with the bottom of a slot in a screw head, said foot portion further having its inwardly sloping sidewalls extending across the entire width of the blade and being engagable with the parallel sidewalls of a screw-head slot said junction of said base and respective inwardly tapered sidewalls defining wedgelike bites which cut a groove in the parallel sidewalls of a screw head slot upon application of a torque to said shank. Advantageously the sides of the foot portion are concave outwardly with respect to the longitudinal axis of said shank. Also the blade portion advantageously includes a bulbous lower portion immediate said foot portion and extending the entire width of said blade. Preferably the bulbous lower portion and saidfoot portion meet at a point of inflection resulting from 'a smoothly radiused transition portion therebetween,

whereby points of stress concentration arising from applying a torque to the shank are generally eliminated. Also the bulbous lower portion preferably has a generally hour glass cross section when viewed in a plane perpendicular to the longitudinal axis of the shank thereby giving the bulbous portion a three-dimensional saddle shape when viewed from either side of the blade, the bulbous portion thereby includes torque transmitting flanges located at the extremities of the blade width.

The screw driver of this invention has been found to be capable of transmitting a torque to a screw head which is greater than twofold the torque that can be transmitted by a conventional screw driver. Also the screw driver of this invention has been found to be resistant to being dislodged once inserted into a screwhead slot and subjected to a torque. In addition, the screw driver of this invention can engage a screw head from an angle other than straight on and still provide its superior torque transmitting qualities, and, lastly, the screw driver of this invention allows the user to position a screw thereon by first engaging one bite of the blade foot means in a screw-head slot and then with a rocking motion engaging the other bite in the slot, whereupon the screw is removably held by the foot portion and easily positioned in a hole not otherwise accessible to a screw.

DESCRIPTION OF THE DRAWING FIG. 1 is an isometric view of one embodiment of the screw driver of this invention.

FIG. 2 is a front view of the blade and shank of the screw driver of FIG. 1.

FIG. 3 is a side view of the blade and shank of FIG. 2.

FIG. 4 is an isometric view of another embodiment of the screw driver of this invention.

FIG. 5 is a front view of the blade and shank of the screw driver of FIG. 4.

FIG. 6 is a side view of the blade and shank of FIG. 5.

FIG. 7 is a cross-sectional plan view taken along line 77 of FIG. 5.

FIG. 8 is an isometric view of a third embodiment of the screw driver of this invention.

FIG. 9 is a frontview of the blade and shank of the screw driver of FIG. 8.

FIG. 10 is a side view of the blade and shank of FIG. 9.

FIG. 1 l is a cross-sectional plan view taken along line 11-11 of FIG. 9.

FIG. 12 is a partial elevational view of the blade of the screw driver of FIG. 4 positioned in a screw head slot.

FIG. 13 is a partial elevational view of the blade of the screw driver of FIG. 1 in a screw-head slot as torque is being applied. thereto.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a screw driver 10 having a handle 12, a shank l4 and a blade 16. The blade 16 includes a generally outwardly or diverging portion 18 and generally converging edges 20. It also includes faces 22 which are located in opposed relationship to each other on opposite sides of the blade. Included in faces 22 in the embodiment shown in FIG. 8 are cutaway portions 24 which cutaway a portion of the bulbous end 25 of the embodiment of FIG. 4. Cutaway portions 24 run substantially the entirelength of the blade and define strengthening ribs 26 on either side of blade 16. Ribs 26 run generally parallel to the longitudinal axis of blade-16. Ribs 26 follow the taper of the sides of blade 16 from the outermost width thereof to the termination of blade 16. Blade 16 terminates in foot portion 28 which includes wedgelike bites 30 on either side thereof. Foot portion 28 is generally isoscelestrapezoidal in cross section diverging outwardly away from the longitudinal axis of the shank and finally terminating at a flat base 32. It should be noted that blade 16 is preferably of a configuration, as shown best in FIGS. and 11, such that the strengthening ribs 26 define, in cooperation with cutaway portions 24, a blade having an hour glass or I-beam-like cross section when viewed in a plane perpendicular to the longitudinal axis of the shaft.

Referring to the simplest embodiment of the present invention, it can be seen that the screw driver of FIG. 1 includes a shank portion 14 which flows smoothly into blade 16 which in turn flows smoothly into foot portion 28. Such an arrangement is specifically designed to avoid creating any sharp corners at intersecting planes which would be points of stress concentration at the juncture of these planes.

In addition the shape of blade 16 of the embodiment of FIG. 4 is such that it abuts the slot of a screw head at an upper point near the top of the screw head as well as at the bottom of the slot. Such an arrangement provides the dual advantages of having wedgelike bites 30 cut a groove into the sidewalls to prevent the screw driver from slipping upwardly out of the slot while at the same time the upper contact point serves to transmit some of the torque from the shank to the head above the constricted transition point thereby alleviating some of the strain thereon as shown in FIG. 12. Advantageously the point of transition 34 in FIG. 12 lies below the upper surface of the screw head. Such an arrangement insures that the angle of the inclined sides of foot portion 28 will define an appropriately angled wedgelike bite portion 30.

In the screw driver of the present invention it should be noted (FIG. 1) that the most effective results are achieved when the angle between the base portion of the foot and its side is acutely sized not to exceed 75 such that when the blade is inserted into the slot of a standard sized screw head the faces 22 are inclined rather than being parallel. Such an arrangement provides a suitable angle for the wedgelike bites which maximizes their effectiveness in cutting into the sidewalls of the screw slots when a torque is applied, as shown in FIG. 13.

Further it should be noted that the embodiment of the screw driver of FIG. 4 includes a blade having a bulbous end portion 25 which serves to reinforce it and resist twisting under the dynamic loading conditions of screw driver uses. More significantly, however, bulbous end portion 25 is geometrically shaped so that stresses caused by the wedgelike bites being engaged into the screw slot sidewalls are transmitted across the screw driver blade and are received and transmitted to the shank by the bulbous blade.

Finally the most preferred embodiment of the screw driver of this invention includes not only the stresstransmitting features of the design which includes the bulbous end portion but includes a blade design which has an I beam or hour glass cross section when viewed in a plane perpendicular to the longitudinal axis of the shaft. Such an arrangement is shown in FIG. 8. In this arrangement the stresses are transmitted from the opposite wedge-like bite portion is laterally across the foot portion and received by the corresponding section of the bulbous blade diametrically opposed thereto. Since the greater torque is transmitted at the edges of the blade as opposed to its center and since therefore the greater material thickness is required thereat, it is necessary to have the blade be its thickest at the edges. However, since on the other hand less torque is transmitted at the center of the blade less material is required. Thus the I beam structure is not only the most efficient it is also the most economical. Another advantage attends the I beam blade configuration however. It is that the screw-head slot is at least partially visible from directly above the screw driver when in use. Thus the screw slot is easily seen and the blade easily inserted therein. Further, the operator can easily see if the screw driver is becoming tilted with respect to the screw head to the extent that the wedgelike bites will no longer grip into the slot sidewalls or whether the screw is going into the right place at the right angle. Also being able to observe the screw slot enables the user to more quickly insert the screw driver blade thereinto before applying torque to the shank. Such an advantage .is particularly significant in mechanized situations such as an assembly line where high speed power equipment is used.

In using the screw driver of this invention one simply inserts the blade into the slot of a screw head with the base of the foot portion extending downwardly thereinto. The screw driver shank is then twisted either manually, with the aid of a handle, or by mechanized means such as an electric motor arrangement, for example, a power drill and chuck.

It should be noted that the screw driver of this invention need not be inserted in the screw head so that the longitudinal axis of the shank is in line with the longitudinal axis of the screw, but rather, the axis of the shank may be slightly angled with respect to the axis of the screw since the wedgelike bites 30 run the entire length of the foot portion 28, and may thus cut into the screw slot sidewalls at any angle. This feature is particularly advantageous when one considers the number of times screw heads are encountered where the head is not accessible from a straight on position, yet considerable torque is needed.

The material of construction of the screw driver can vary widely, however, a high quality steel is preferred. One such steel is designated as AISI no. A 3150 and is a high carbon steel having about 0.480.53 percent carbon, 0.70-030 percent manganese, 1.10-1.40 percent nickel and 0.70-0.90 percent chromium contained therein among its principal additives.

It should be recognized that although the drawing depicts a square shank and a round handle for the screw driver shown therein any suitable configuration can be employed in the practice of this invention.

Having thus described the invention what is claimed 1. A screw driver comprising a shank and blade integral therewith, said blade having opposed major faces which are arcuately bowed outwardly to define a bulbous lower portion, said bulbous lower portion extending the entire width of said blade, said blade further including a smoothly radiused transition portion integral with a foot portion, said foot portion protruding outwardly away from the longitudinal axis of said shank to provide a gripping means, said foot portion further defining the lowermost portion of said blade and being generally isosceles-trapezoidal in side cross section with its base lying furthest from the shank in a substantially flat plane perpendicular to the axis of said shank at the lowest extremity of the blade, thereby being engagable with the bottom of the slot in a screw head, said foot portion further having its inwardly tapered sidewalls extending across the entire width of the blade and being engagable with the parallel sidewalls of a screwv head slot, said base of said foot portion and said respective inwardly tapered sidewalls defining wedge-like bites comprising said gripping means engagable with opposed sides of a screw slot to removably hold a screw thereon and also cut a groove in the parallel sidewalls of a screw head slot upon application of a torque to said shank.

2. The screw driver of claim 1 wherein said bulbous lower portion has a generally hour-glass cross section when viewed in a plane perpendicular to the longitudinal axis of said shank thereby giving said bulbous portion a three-dimensional saddle shape when viewed from either side of said blade, said bulbous portion thereby including torque-transmitting flanges located at the extremeties of said blade width. 

1. A screw driver comprising a shank and blade integral therewith, said blade having opposed major faces which are arcuately bowed outwardly to define a bulbous lower portion, said bulbous lower portion extending the entire width of said blade, said blade further including a smoothly radiused transition portion integral with a foot portion, said foot portion protruding outwardly away from the longitudinal axis of said shank to provide a gripping means, said foot portion further defining the lowermost portion of said blade and being generally isosceles-trapezoidal in side cross section with its base lying furthest from the shank in a substantially flat plane perpendicular to the axis of said shank at the lowest extremity of the blade, thereby being engagable with the bottom of the slot in a screw head, said foot portion further having its inwardly tapered sidewalls extending across the entire width of the blade and being engagable with the parallel sidewalls of a screw head slot, said base of said foot portion and said respective inwardly tapered sidewalls defining wedge-like bites comprising said gripping means engagable with opposed sides of a screw slot to removably hold a screw thereon and also cut a groove in the parallel sidewalls of a screw head slot upon application of a torque to said shank.
 2. The screw driver of claim 1 wherein said bulbous lower portion has a generally hour-glass cross section when viewed in a plane perpendicular to the longitudinal axis of said shank thereby giving said bulbous portion a three-dimensional saddle shape when viewed from either side of said blade, said bulbous portion thereby including torque-transmitting flanges located at the extremeties of said blade width. 